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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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LUCIA AND ATREVIDA GLACIERS                            71
near the base. There were a few crevasses, dipping like joint planes at an angle of 5 or 10 from the horizontal and suggesting differential ice movement. At the top of the 200 foot ice slope there was a dense alder thicket with bushes estimated to be fifteen or twenty years old. We are inclined to interpret the slight crevassing of the ice cliff as the beginning of the advance and profound breaking which were observed nine months later.
Professor Russell crossed Atrevida Glacier in 1890, starting at the point of emergence of Esker Stream, with his entire outfit. From his description we are led to infer that the Atrevida was in essentially the same condition in 1905 as in 1890. One of the photographs illustrating his reportx shows the glacier surface covered with ablation moraine; another shows the ice cave from which Esker stream emerges and we could notice scarcely any difference in its form in August, 1905. Russell's description of the conditions in 1890 was as follows2 "The waters, brown and turbid with sediment, welled out of a cavern at the foot of an ice precipice 200 feet high, and formed a roaring stream too deep and too swift for fording. . . . The dark-colored ice, mixed with stones and dirt, might easily be mistaken for stratified rock, but the dirt discoloring the ice is almost entirely superficial. The crest of the cliff is formed of debris, and is the edge of the sheet of stones and dirt covering the general surface of the glacier. Owing to the constant melting, stones and boulders are continually loosened to rattle down the steep slope and plunge into the water beneath."
There is every reason to believe that the glacier had changed very little for many years before Russell's visit. Its piedmont portion must have been in a stagnant state for at least a half century before 1905, otherwise the ablation moraine and its forest could not have developed. That it had not been notably more expanded for an even greater length of time was proved by the presence of a mature forest growing up to the very margin of the moraine-covered ice. No notable recent recession had taken place, for there was only a very narrow area along this margin in which the forest did not grow. From the evidence that we possess we feel warranted in inferring a long period of stagnation, with no notable advance or recession for several decades, and probably for more than half a century. Up to the autumn of 1905 the Atrevida was a fine example of a valley glacier with a piedmont terminus completely covered with ablation moraine and in the outer portion so stagnant that it bore a dense growth of vegetation. No one would have expected that such a glacier would suddenly spring into activity, and such a thought never occurred to us even when, in June 1906, the senior author approached the Atrevida with the purpose of traversing a route westward to the Malaspina along the line followed by Russell in 1890 and by the junior author in August, 1905.
The Advance of 1906. As the Geological Survey party approached the margin of Atrevida Glacier early in June, 1906, never dreaming of change, the first surprise came when at a distance of several miles a jagged ice cliff was seen where nine months earlier there was a low, moraine-covered ice margin, bearing forest; and later investigation showed that the entire glacier, with the exception of the outermost portion, was utterly transformed and quite impassable. A bird's-eye view of the entire glacier was obtained from the crest of Amphitheatre Knob (Pis. XXVI, XXVII), which rises directly above the eastern margin of the Atrevida, and early in August a visit was made, via Floral
i Busaell, I. C., An Expedition to Mount St Elks, Alaska, Nat Geog. Mag., Vol. HI. 1801, PI. X. i Nat. Geog. Mag., Vol. m, 1891, pp. 94-6.